Production of Environmentally Friendly Polyester by Hydrogenation of Poly(butylene terephthalate) over Rh–Pt Catalysts Supported on Carbon Black and Recovery by a Compressed CO₂ Antisolvent Technique

Abstract

The direct hydrogenation of poly­(butylene terephthalate) (PBT) using 1,1,1,3,3,3-hexafluro-2-propanol (HFIP) as the solvent to environmentally friendly polyester poly­(butylene-1,4-cyclohexanedicarboxylate) (PBC) using a VulcanXC72-supported 2.5 wt % rhodium (Rh) and 2.5 wt % platinum (Pt) catalyst synthesized via the polyol method was studied. The pathway for the complete hydrogenation of PBT was suggested by observing the effects of temperature, H2 pressure, and reaction time on conversion and selectivity. Rh–Pt bimetallic catalysts were found to be superior to monometallic Rh catalysts for the hydrogenation of PBT, owing to the stronger aromatic ring adsorption ability of Rh coupled with Pt, assisting effective H2 spillover. At 50 °C and a H2 pressure of 6.89 MPa, PBT could be completely hydrogenated to PBC in 60 min, and PBC could be effectively recovered using a compressed CO2 antisolvent technique at room temperature after hydrogenation.

Chemical upcycling of polymers

“…It finds application as an engineering plastic that is in widespread use in household items such as coffeemakers, hairdryers, irons or plug sockets. In 2020, Tan et al [44] published the development of a hydrogenation process of PBT to poly(butylene-1,4-cyclohexanedicarboxylate) (PBC) (scheme 2). PBC is a biodegradable polyester that can be used as a scaffold in tissue engineering [45] or it can be converted into polyurethanes for shape memory materials [46].…”

On-Water Hydrogenation of Polyethylene Terephthalate to Environmentally Friendly Polyester by the Catalyst Rh2.5Pt2.5/SBA-15

“…Therefore, the direct hydrogenation of PET to PECHD is highly desirable and has been previously reported by our group using a Rh–Pt bimetallic catalyst supported on carbon black, Vulcan XC-72, in the solvent 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) . Although a 100% selective hydrogenation of PET to PECHD was reported at mild reaction conditions and after hydrogenation the environmentally unfriendly solvent HFIP could be recovered to a high extent and recycled for subsequent runs via supercritical CO 2 antisolvent separation, the use of HFIP still posed an environmental hazard and the major drawback of the proposed process still remained regarding the use of HFIP . Because PET is completely insoluble in all common organic solvents, the processing of PET without using HFIP would then require PET to be melted completely to its liquid state prior to its processing, which would once again require significant energy consumption.…”

“…14 Although a 100% selective hydrogenation of PET to PECHD was reported at mild reaction conditions and after hydrogenation the environ- mentally unfriendly solvent HFIP could be recovered to a high extent and recycled for subsequent runs via supercritical CO 2 antisolvent separation, the use of HFIP still posed an environmental hazard and the major drawback of the proposed process still remained regarding the use of HFIP. 15 Because PET is completely insoluble in all common organic solvents, the processing of PET without using HFIP would then require PET to be melted completely to its liquid state prior to its processing, which would once again require significant energy consumption. The pertinent objective of this study was therefore to develop a process possessing the capability of completely hydrogenating PET in its solid state but using a more environmentally friendly solvent at mild reaction conditions.…”